1. Field of the Invention
This invention relates to apparatus and method providing alignment measures for each of the wheels on a chassis supported by a steerable wheel pair and a nonsteerable pair, and more particularly such apparatus and method wherein wheel toe measurement is provided relative to either the chassis centerline or the average rear wheel rolling direction.
2. Description of the Prior Art
Apparatus providing rearwardly projected light beams for use in determining the inclinations of front steerable wheels relative to the axis of rotation of one of the rear nonsteerable wheels may be found in U.S. Pat. Nos. 4,154,531, Roberts, Jr. et al, issued May 15, 1979; 4,150,897, Roberts, Jr. et al, issued Apr. 24, 1979; 4,130,362, Lill et al, issued Dec. 19, 1978; and 4,097,157, Lill, issued June 27, 1978, all of which are currently assigned to the assignee of record of the invention disclosed herein. The 4,154,531 patent discloses apparatus wherein the rearwardly projected beam is caused to swing through a predetermined angle. The beam is reflected by a mirror mounted in predetermined relationship with the axis of rotation of one of the rear nonsteerable wheels so that the oscillating beam is reflected back to a target mounted on the front steerable wheel on the same side of the vehicle. The time relationship between the instants when the projected oscillating beam is received by light sensitive devices when reflected toward a front wheel mounted target is used to determine the inclination of the front steerable wheel in the horizontal or toe plane.
The 4,130,362 patent disclosure provides a multiplicity of beams projected at known angles relative to a reference angle from a projector mounted on one of the steerable front wheels of the vehicle. A mirror mounted on the rear wheel on the same side of the vehicle in predetermined relationship with the axis of rotation of the rear wheel reflects one of the projected beams back to the front wheel assembly. The reflected and received beam from the multiplicity of beams determines the inclination of the front wheel in the horizontal or toe plane.
4,097,157 patent disclosure makes reference to a rearwardly projected beam which is reflected by a mirror mounted in predetermined relationship with a nonsteerable wheel on the same side of the vehicle. The reflected beam is received at an encoding target which is mounted on the front wheel on the same side of the vehicle to provide an indication of the inclination of the front wheel in the horizontal or toe plane relative to the axis of rotation of the rear wheel.
The 4,150,897 patent disclosure relates to a rearwardly transmitted light beam from a front steerable wheel mounted assembly which is reflected by a rear wheel mounted mirror having predetermined orientation relative to the axis of rotation of the rear wheel. The front steerable wheels are adjusted in steering direction until the beam reflected from the rear wheel mounted mirror strikes a calibration point on the front wheel mounted assembly. The mirror on the rear wheel is then moved laterally so that the projected beam falls on a scale on the mirror at a point which is related to the desired toe setting for the front steerable wheels of the vehicle. The front steerable wheel is adjusted in toe so that the projected beam moves to a desired location on the rear mirror thereby setting known front wheel toe into the one front steerable wheel. The toe of the other front steerable wheel is set in the usual manner to obtain the desired total front steerable wheel toe. The apparatus automatically adjusts for different vehicle wheel spacings.
An optical system is disclosed in U.S. Pat. No. 4,058,903, Wilkerson, issued Nov. 22, 1977, in which sighting tubes and scales are provided at both the front and the rear of the vehicle. These scales and sighting tubes are supported by structure adjacent to the vehicle. The scales are sighted through the tubes so that information relating to the angular orientation of each wheel pair axis relative to a vehicle steering axis is obtained. The stated purpose of the apparatus is to ascertain certain faults in the alignment of the vehicle frame rather than to align the wheels of the vehicle.
U.S. Pat. No. 3,855,709, Hirmann, issued Dec. 24, 1974 discloses a system which includes an electromechanical computer which ascertains the centerline of a vehicle and makes wheel alignment measurements relative to the centerline. The apparatus disclosed by Hirmann is fixed in position surrounding a space into which a vehicle is driven. The alignment characteristics of the vehicle wheels are thereafter measured by the apparatus fixed in position and surrounding the vehicle.
An apparatus is disclosed in U.S. Pat. No. 3,091,862, MacMillan, issued June 4, 1963, in which a pair of right and left hand targets are positioned in known relationship with the rear wheels on a vehicle. Sighting tubes are provided which are aligned with the planes parallel to the steerable front wheel planes and which are directed rearwardly toward the targets on each side of the vehicle. The steering angle of the front wheels is adjusted until similar points on the rear positioned targets are observed through the sight tubes. The wheels are thereby aligned straight ahead relative to the rear wheels and the steering wheel inside the car may be adjusted to a centered position by well known mechanical adjustments.